Valve actuation controlling apparatus and method for engine

ABSTRACT

After commanding an engine to stop, an electronic controller controls a variable working-angle control mechanism to increase the working angle of an intake valve in preparation for restarting of the engine. In the case of an automatic stop, which is followed by restarting of the engine in a relatively short time, the working angle of the intake valve is set to the maximum working angle of the variable working-angle control mechanism, which maximizing decompression. In a manual stop, it is necessary to allow for both hot start and cold start. Also, in the manual stop, a target working angle when the engine is stopped is set less than that of a case of the automatic stop. Thus, the starting characteristic is prevented from being degraded by increased friction of engine parts during a cold start, and knocking is prevented from occurring due to a high compression ratio in a cylinder during a hot start.

BACKGROUND OF THE INVENTION

The present invention relates to a valve actuation controlling apparatusand method applied to an engine equipped with a variable working-anglecontrol mechanism which varies the working angle of intake valves.

Engines such as vehicle engines are equipped with variable valvemechanisms which vary valve characteristics of intake valves and exhaustvalves. Among variable valve mechanisms proposed recently, there arevariable valve lift and working-angle control mechanisms which varyvalve lifts and working angles of intake and exhaust valves.

Japanese Laid-Open Patent Publications No. 2002-89303 and No. 2002-61522each disclose a valve actuation controlling apparatus that presets thevalve actuation of intake valves to be suitable for securing enginestarting characteristics immediately before the engine stops, therebypreparing for a next engine start. As shown in FIG. 8, immediatelybefore the engine stops, that is after commanding the engine to stop,the valve actuation controlling apparatus as disclosed in JapaneseLaid-Open Patent Publications No. 2002-89303 and No. 2002-61522 reducesthe valve lift and the working angle θ of the intake valves compared tothose during idling of the engine, and advances the center φ of theworking angle. If the working angle θ is reduced and the working anglecenter φ is advanced, intake valve closing time IVC is advanced farahead of a bottom dead center BDC and a compression ratio of air in acylinder is reduced, causing decompression to occur during starting ofthe engine. Also, if the lift is reduced and valve-opening area of theintake valve when opened is reduced, velocity of air flow into thecylinder is increased, thereby intensifying air flow in the cylinderduring starting of the engine.

It is true that decompression and intensified cylinder air flow arefavorable to improvement of engine starting characteristics. However,the above setting of the valve actuation of intake valves does notalways ensure proper engine starting characteristics depending on enginestarting conditions.

For example, during a very cold start in which engine parts encounterhigh friction, working angle θ that is less than that of idling mayresult in a shortage of intake air, making it impossible to generatesufficient torque to counteract the increased friction. On the otherhand, an attempt to intensify air flow in the cylinder will cause heatfrom friction between air and the intake valve, etc. to raisecompression end temperature (temperature at the top dead center) of theair drawn into the cylinder, increasing the likelihood of knockingduring a hot start. Thus, reducing the lift and working angle θ of theintake valves immediately before the engine stops do not always ensureproper engine starting characteristics.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to providevalve actuation controlling apparatus and method that improve enginestarting characteristics.

To achieve the foregoing and other objectives and in accordance with thepurpose of the present invention, a valve actuation controllingapparatus applied to an engine equipped with a variable working-anglecontrol mechanism which varies working angle of an intake valve isprovided. After commanding the engine to stop, the valve actuationcontrolling apparatus controls the variable working-angle controlmechanism to increase the working angle of the intake valve inpreparation for restarting of the engine.

The present invention provides anther valve actuation controllingapparatus applied to an engine equipped with a variable working-anglecontrol mechanism which varies working angle of an intake valve. Aftercommanding the engine to stop, the valve actuation controlling apparatuscontrols the variable working-angle control mechanism to increase theworking angle of the intake valve in preparation for restarting of theengine, and varies the increased working angle according to whether astopping requirement of the engine is satisfied.

The present invention also provides an engine having a variableworking-angle control mechanism which varies working angle of an intakevalve and a valve actuation controlling apparatus. After commanding theengine to stop, the valve actuation controlling apparatus controls thevariable working-angle control mechanism to increase the working angleof the intake valve in preparation for restarting of the engine.

The present invention provides another engine having a variableworking-angle control mechanism which varies working angle of an intakevalve and a valve actuation controlling apparatus. After commanding theengine to stop, the valve actuation controlling apparatus controls thevariable working-angle control mechanism to increase the working angleof the intake valve in preparation for restarting of the engine, andvaries the increased working angle according to whether a stoppingrequirement of the engine is satisfied.

Further, the present invention provides a valve actuation controllingmethod applied to an engine equipped with a variable working-anglecontrol mechanism which varies working angle of an intake valve. Themethod includes controlling the variable working-angle control mechanismto increase the working angle of the intake valve in preparation forrestarting of the engine, after commanding the engine to stop.

The present invention provides another valve actuation controllingmethod applied to an engine equipped with a variable working-anglecontrol mechanism which varies working angle of an intake valve. Themethod includes: controlling the variable working-angle controlmechanism to increase the working angle of the intake valve inpreparation for restarting of the engine, after commanding the engine tostop; and varying the increased working angle according to whether astopping requirement of the engine is satisfied.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1 is a schematic diagram showing an engine control system accordingto one embodiment of the present invention;

FIG. 2(a) is a graph showing changes in valve actuation in a variablephase mechanism;

FIG. 2(b) is a graph showing changes in valve actuation in a variableworking-angle control mechanism;

FIG. 3 is a diagram outlining automatic stop/restart control;

FIG. 4 is a flowchart of a working angle setting process during enginestopping period;

FIG. 5(a) is a diagram showing a setting of working angle of the intakevalve after a manual engine stop made by the automatic stop/restartcontrol;

FIG. 5(b) is a diagram showing a setting of the working angle of theintake valve after an automatic engine stop made by the automaticstop/restart control;

FIG. 6 is a time chart showing a control in a case where the ignitionswitch is turned off;

FIG. 7 is a time chart showing a control in a case where the engine isautomatically stopped; and

FIG. 8 is a diagram showing valve actuation setting of an intake valvewhen an engine stops in a case of a prior art valve actuationcontrolling apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described in detail belowwith reference to the drawings.

As shown in FIG. 1, an engine 10 includes an intake passage 11, acombustion chamber 12, and an exhaust passage 13. Installed in theintake passage 11 are an air flowmeter 14 which detects an air flow ratein the intake passage 11 and a throttle valve 15 which changes the airflow rate by changing the flow area of the intake passage 11. The intakepassage 11 is connected to the combustion chamber 12 via an intake valve16. The combustion chamber 12 is connected to the exhaust passage 13 viaan exhaust valve 17. The intake valve 16 and exhaust valve 17 are drivenaccording to rotation of the engine 10. The intake valve 16 opens andcloses the intake passage 11 to the combustion chamber 12, and theexhaust valve 17 opens and closes the exhaust passage 13 to thecombustion chamber 12.

A valve operating system of the intake valve 16 has a variable phasemechanism 18 and a variable working-angle control mechanism 19. Thevariable phase mechanism 18 continuously changes a working angle centerφ of the intake valve 16 as shown in FIG. 2 (a). The variable phasemechanism 18 employed in this engine 10 changes the working angle centerφ by changing a rotational phase of a camshaft with respect to acrankshaft. The variable working-angle control mechanism 19 continuouslychanges the working angle θ of the intake valve 16 as shown in FIG.2(b). The variable working-angle control mechanism 19 increases the liftof the intake valve 16 in accordance with an increase of the workingangle θ, and decreases the lift of the intake valve 16 in accordancewith a decrease of the working angle θ. The working angle of the intakevalve 16 is the number of degrees the intake valve 16 stays open.

Both of the variable phase mechanism 18 and the variable working-anglecontrol mechanism 19 are driven hydraulically. The hydraulic power issupplied from an oil pump that is driven by rotation of the crankshaftof the engine 10.

Various types of control over the engine 10 configured as describedabove are performed by an electronic controller 20. The electroniccontroller 20 is equipped with a central processing unit (CPU) whichruns various computational processes for controlling the engine 10, aread-only memory (ROM) which stores control programs and data, a randomaccess memory which records computational results from the CPU and datafrom sensors, and input and output ports used to exchange data withexternal devices.

The input ports of the electronic controller 20 are connected with theair flowmeter 14, a throttle sensor 21, a valve timing sensor 22 (VTsensor 22), and a valve lift sensor (VL sensor 23). The throttle sensor21 detects the opening degree (throttle opening degree Ta) of thethrottle valve 15. The VT sensor 22 detects the current working anglecenter φ of the intake valve 16. The VL sensor 23 detects the currentworking angle θ of the intake valve 16. The input ports of theelectronic controller 20 are connected with various sensors which detectoperating condition of the engine 10 and driving-condition of thevehicle.

The output ports of the electronic controller 20 are connected withvarious actuators used to control the engine 10 as well as with thethrottle valve 15, the variable phase mechanism 18, and the variableworking-angle control mechanism 19. The electronic controller 20controls the actuators based on detection results produced by thevarious sensors, and thereby performs various types of control over theengine 10.

For example, valve actuation control of the intake valve 16 is performedas follows. First, the electronic controller 20 calculates target valuesfor the working angle center φ and the working angle θ of the intakevalve 16 suitable for the current operating state based on therotational speed of the engine and depression of an accelerator pedaldetected by sensors. The electronic controller 20 performs feedbackcontrol of the variable phase mechanism 18 and the variableworking-angle control mechanism 19 such that the current working anglecenter φ and working angle θ detected by the VT sensor 22 and the VLsensor 23 of the intake valve 16 seek the calculated respective targetvalues. This makes it possible to obtain optimum valve actuation of theintake valve 16 according to the current operating state of the engine.

If the working angle θ and the lift of the intake valve 16 are changedby the variable working-angle control mechanism 19, the volume of airintroduced into the combustion chamber 12 (intake air amount Ga) ischanged as well. To deal with this situation, the electronic controller20 controls the opening degree of the throttle valve 15 along withcontrol of the working angle θ. This secures a required intake airamount Ga regardless of changes made by the variable working-anglecontrol mechanism 19 to the working angle θ and the lift of the intakevalve 16.

If idling continues for a relatively long period of time while waitingfor traffic lights to change, automatic stop/restart control, i.e.,“automatic idling stop control”, is performed, which involves stoppingthe engine 10 automatically, waiting in a stopped state, and restartingthe engine in response to the driver's action to start the vehicle. Theautomatic stop/restart control is performed by the electronic controller20, and will be outlined below with reference to FIG. 3.

When the driver turns on an ignition switch, so that the electroniccontroller 20 is activated, the electronic controller 20 sets controlmode to Mode 0, which represents normal engine-stopped state. In Mode 0,if the driver sets the ignition switch to a Start position, the engine10 starts being cranked. When the engine 10 is started successfully, thecontrol mode of the electronic controller 20 shifts to Mode 1, whichrepresents normal engine-operating state.

If the ignition switch is turned off during normal operation of theengine 10 in Mode 1, the electronic controller 20 performs a normalengine stopping process to stop the engine 10 and shifts to Mode 0.After performing necessary stop processes, the electronic controller 20cuts off power to itself.

On the other hand, if automatic stopping requirements of the engine 10are satisfied during normal engine operation in Mode 1, the electroniccontroller 20 shifts to Mode 2 in which it performs an engine stopprocess to stop the engine 10 automatically. With the engine 10 of thisembodiment, the automatic stopping requirements are satisfied, forexample, if all the following conditions (a1) to (a6) are met.

(a1) The depression of the accelerator pedal is 0.

(a2) The vehicle speed is equal to or lower than a predetermined speed.

(a3) The brake pedal is depressed.

(a4) Coolant temperature is equal to or higher than a predeterminedtemperature Ta and the engine 10 has been warmed up.

(a5) Hydraulic fluid temperature of an automatic transmission is equalto or higher than a predetermined temperature.

(a6) Car battery level is equal to or above a predetermined value.

As the control mode shifts to Mode 2, the electronic controller 20 stopsfuel supply, and thereby stops the engine 10. When it is confirmed thatthe engine 10 has stopped completely, the control mode of the electroniccontroller 20 shifts to Mode 3, which represents engine-stopped statebrought about by the automatic stop/restart control.

In Mode 3, when the engine 10 is on standby and in a stopped state, ifrestart requirements of the engine 10 are satisfied, the electroniccontroller 20 shifts to Mode 4 in which it performs a restart process torestart the engine 10 automatically. With the engine 10 of thisembodiment, the restart requirements are satisfied, for example, if anyof the following conditions (b1) to (b4) is met.

(b1) The brake pedal is released.

(b2) The accelerator pedal is depressed.

(b3) A shift is made from P (parking) or N (neutral) range to anotherrange.

(b4) The car battery level is below a predetermined value.

As the control mode shifts to Mode 4, the engine 10 is restarted. Whenthe engine 10 is restarted successfully, the control mode of theelectronic controller 20 shifts to Mode 1.

In Mode 3, i.e., in an engine-stopped state brought about by theautomatic stop/restart control, if a malfunction occurs duringrestarting of the engine 10 in Mode 4 due to turning off of the ignitionswitch or an abnormality in the system, the electronic controller 20shifts forcibly to Mode 0. In that case, the engine 10 is restarted onlyif the driver operates the ignition switch directly. That is, the engine10 is not restarted automatically.

(Engine Stop Time Working Angle Setting Process)

With the engine 10 of this embodiment, when the engine 10 stops, theworking angle θ of the intake valve 16 is set to an optimum value inpreparation for the next restarting of the engine 10. Details of thestop-time working angle setting process will be described below withreference to FIGS. 4 to 7.

The engine 10 of this embodiment can be stopped in two ways: manual stopvia deactivation of the ignition switch and automatic stop via theautomatic stop/restart control. In the case of the automatic stop, whichis followed by restarting in a relatively short time, the restarting isa hot start in which the engine 10 is restarted in a sufficiently hotstate. On the other hand, in the case of the manual stop, which is madethrough deactivation of the ignition switch, it is necessary to allowfor both hot start and cold start because it is difficult to predictsituations in which the engine is started.

Thus, according to this embodiment, the working angle θ of the intakevalve 16 is varied between the automatic stop based on automaticstop/restart control and manual stop based on deactivation of theignition switch. Thus, an optimum working angle θ is preset for theintake valve 16 according to expected situations in which the engine 10will be started, taking into consideration the difference betweenautomatic stop and manual stop.

FIG. 4 shows a flowchart of the stop-time working angle setting processaccording to this embodiment. The electronic controller 20 determines inStep 100 whether the engine 10 is in an automatically stopped state. Ifthe engine 10 is in an automatically stopped state (S100: YES), theelectronic controller 20 sets the target value of the working angle θ ofthe intake valve 16, i.e., a stop-time target working angle θt which isset during a stop, to a maximum working angle θmax (θmax=260° CA in thisengine 10) which is the upper limit of a working angle range of thevariable working-angle control mechanism 19 in step 102. Thereafter, theelectronic controller 20 proceeds to step 110. If the engine 10 is notin an automatically stopped state (S100: NO), the electronic controller20 goes to step 104.

At step 104, the electronic controller 20 determines whether the engine10 is currently in a manually stopped state based on deactivation of theignition switch. If the engine 10 is in a manually stopped state (S104:YES), the electronic controller 20 sets the stop-time target workingangle θt to a relatively large value (e.g., 200° CA) in step 106, andthen it goes to step 110. If the engine 10 is not in a manually stoppedstate (S104: NO), i.e., if the engine 10 is not currently stopped, theelectronic controller 20 temporarily suspends the routine. In this case,normal working angle control is performed according to theengine-operating state as described above.

In step 110, the electronic controller 20 controls the variableworking-angle control mechanism 19 such that the current working angle θof the intake valve 16 seeks the target working angle θt set in step 102or step 106. Immediately before a stop, the engine 10 is normallyoperated under low loads and the working angle θ of the intake valve 16is set to a relatively small value. Thus, the working angle θ of theintake valve 16 is increased through the working angle control. At thesame time, the electronic controller 20 also changes the working anglecenter φ of the intake valve 16 as required.

If the working angle θ of the intake valve 16 is increased, the intakeair amount Ga changes accordingly. This increases or decreasescompression torque of the air in the cylinder, and may cause variationsin rotational speed of the engine. To deal with this situation, theelectronic controller 20 performs cooperative control in step 112 toregulate the throttle opening Ta in response to increases in the workingangle θ of the intake valve 16, and then the electronic controller 20temporarily suspends the routine. The cooperative control involvesdecreasing the throttle opening Ta to curb any increase in the intakeair amount Ga resulting from increases in the working angle θ of theintake valve 16, and increasing the throttle opening Ta to check anydecrease in the intake air amount Ga resulting from increases in theworking angle θ of the intake valve 16.

Even if the intake air amount Ga is not kept constant by the cooperativecontrol of the throttle opening Ta while the engine is stopped, it ispossible to reduce variations in the rotational speed of the engine,provided that the changes in the intake air amount Ga resulting fromincreases in the working angle θ is curbed through changes in thethrottle opening Ta. The electronic controller 20 executes the aboveroutine periodically while it is active.

After a manual stop, the working angle θ of the intake valve 16 is setto a relatively large value (e.g., 200° CA) by the stop-time workingangle setting process. In so doing, the valve closing time IVC of theintake valve 16 is set to a point relatively early in the middle periodof the compression stroke as shown in FIG. 5(a). Since both hot startand cold start are anticipated in the case of restarting after a manualstop as described above, it is necessary to set working angle θ whichcan accommodate both hot start and cold start properly.

In the case of a hot start, an excessive volume of the intake air amountGa raises the compression end temperature, i.e., an excessive volume ofthe intake air amount Ga increases a temperature rise in the cylinderdue to adiabatic compression in the cylinder when the top dead center isreached. This may cause knocking. To deal with this situation, it isnecessary to lower the compression ratio of air in the cylinder bydelaying the valve closing time IVC of the intake valve 16 relative tothe bottom dead center BDC and thereby returning part of the air drawnonce into the cylinder to the intake passage 11 along with ascent of thepiston during the compression stroke.

In the case of a cold start, it is necessary to secure an intake airamount Ga equal to or larger than a certain volume in order to generatesufficient torque to counteract the friction of parts of the engine 10increased by decreased lubricant viscosity and the like. That is, evenwhen reducing the compression ratio of air in the cylinder, the delay inthe valve closing time IVC of the intake valve 16 caused by an increasein the working angle θ should be kept within certain limits in order tosecure the sufficient volume of intake air needed to make a cold start.

Thus, at the time of a manual stop of the engine 10, the target workingangle θt of the intake valve 16 is set such that a compression ratio ofair in the cylinder (combustion chamber 12) is equal to or lower thanthe upper limit of a range in which knocking is avoided during a hotstart of the engine 10, and is equal to or higher than the lower limitof a range in which sufficient torque is generated during a cold startof the engine 10. Consequently, during restarting, the engine 10 can bestarted under increased friction in case of a cold start, and knockingcan be avoided in case of a hot start. Also, decompression occurs due tothe reduced compression ratio.

In order to permit a delay in the valve closing time IVC, the workingangle center φ of the intake valve 16 is delayed more than duringlow-load operation of the engine 10 such as idling.

On the other hand, after an automatic stop of the engine 10, the workingangle θ of the intake valve 16 is set to the maximum working angle θmaxby the stop-time working angle setting process. The valve closing timeIVC of the intake valve 16 is set in the middle period of thecompression stroke, lagging greatly behind the bottom dead center BDC asshown in FIG. 5(b).

After an automatic stop, since the engine 10 is restarted in arelatively short time, the restarting is expected to be a hot start.Since only a hot start is expected, the engine 10 requires only smalltorque during starting, obviating the need to secure a large intake airamount Ga. Consequently, the valve closing time IVC of the intake valve16 is allowed to be delayed greatly in order to maximize decompression.Thus, the working angle θ of the intake valve 16 is set to the maximumworking angle θmax, allowing the valve closing time IVC to be delayed tothe maximum extent possible. Incidentally, the working angle center φ ofthe intake valve 16 is set to the same phase as during the manual stop.

FIG. 6 shows in a manual stop in the stop-time working angle settingprocess. As shown in FIG. 6, if the ignition switch is turned off attime t1, i.e., if an engine stop command is given manually, the workingangle θ of the intake valve 16 is increased gradually to the targetworking angle θt (200° CA) . At the same time, the valve closing timeIVC of the intake valve 16 is gradually delayed toward the bottom deadcenter BDC.

At this time, if the throttle opening Ta is fixed, increases in theworking angle θ result in increases in the intake air amount Ga asindicated by an alternate long and short dash line in FIG. 6. However,since the throttle opening Ta is decreased gradually by the cooperativecontrol with increases in the working angle θ, the increases in theintake air amount Ga are curbed.

When the valve closing time IVC of the intake valve 16 is delayedrelative to the bottom dead center BDC at time t2, the intake air amountGa decreases with further increases in the working angle θ. However,after time t2, the cooperative control gradually increases the throttleopening Ta in accordance with increases in the working angle θ, andthereby curbs the decreases in the intake air amount Ga.

At time t3, when the working angle θ of the intake valve 16 reaches thetarget working angle θt (e.g., 200° CA), the working angle θ stopsincreasing and is held at the target working angle θt. When it isconfirmed that the working angle θ has stopped increasing to the targetworking angle θt and that the engine 10 has stopped completely, theelectronic controller 20 finishes the engine stop process and cuts offpower to itself.

FIG. 7 shows in an automatic stop in the stop-time working angle settingprocess. As shown in FIG. 7, at time t4, if the automatic stoppingrequirements are satisfied and the electronic controller 20 shifts fromMode 1 to Mode 2, i.e., if an engine stop command is given by theautomatic stop/restart control, the working angle θ of the intake valve16 increases gradually to the maximum working angle θmax (260° CA),i.e., to the target working angle θt. At the same time, the valveclosing time IVC of the intake valve 16 is delayed toward the bottomdead center BDC, and the intake air amount Ga is increased accordingly.Thus, the cooperative control gradually decreases the throttle openingTa to curb the increases in the intake air amount Ga.

When the valve closing time IVC of the intake valve 16 is delayedrelative to the bottom dead center BDC at time t5, the intake air amountGa decreases with further increases in the working angle θ. Thus, thecooperative control gradually increases the throttle opening Ta to curbthe decreases in the intake air amount Ga.

At time t6, when the working angle θ of the intake valve 16 reaches themaximum working angle θmax, the working angle θ stops increasing and isheld at the maximum working angle θmax. When it is confirmed that theworking angle θ has stopped increasing to the target working angle θtand that the engine 10 has stopped completely, the electronic controller20 switches to Mode 3 and makes the engine 10 standby in a stopped stateuntil the restart requirements are satisfied.

The embodiment described above has the following advantages.

(1) After commanding the engine 10 to stop, the electronic controller 20according to this embodiment increases the working angle θ of the intakevalve 16 far more greatly than for a low-load operation, in preparationfor restarting the engine 10. Specifically, the working angle θ of theintake valve 16 is increased to such an extent that the valve closingtime IVC of the intake valve 16 coincides with the middle period of thecompression stroke. Consequently, the compression ratio of air in thecylinder is reduced, causing decompression to occur. This reduces thetorque required for the crankshaft to rotate. The restart of the engine10 is therefore facilitated. Also, since decompression occurs even ifintake air is not throttled by the intake valve 16, it is possible toprevent compression end temperature from rising due to frictional heatand to avoid eventual knocking during a hot start of the engine 10.

(2) According to this embodiment, the target working angle θt forincreases in the working angle θ is varied between automatic stop andmanual stop of the engine 10. More specifically, in the case of theautomatic stop of the engine 10, the target working angle θt is set tothe maximum working angle θmax of the variable working-angle controlmechanism 19. In the case of the manual stop of the engine 10, thetarget working angle θt is set such that the compression ratio of air inthe cylinder is equal to or lower than the upper limit of a range inwhich knocking can be avoided during a hot start of the engine, and isequal to or higher than the lower limit of a range in which sufficienttorque can be generated during a cold start of the engine. This makes itpossible to set a desirable working angle according to conceivablesituations in which the engine 10 will be started in the case of bothautomatic stop and manual stop.

(3) According to this embodiment, cooperative control of the intakevalve 16 is performed in response to increases in the working angle θ ofthe intake valve 16 at the time of an engine stop. This reducesvariations in the intake air amount Ga resulting from increases in theworking angle θ of the intake valve 16 during the engine stop, making itpossible to reduce variations in the rotational speed of the engine 10caused by changes in the compression ratio.

(4) According to this embodiment, the working angle center φ of theintake valve 16 is changed along with increases in the working angle θof the intake valve 16 at the time of the engine stop. This makes thevalve actuation of the intake valve 16 at the time of restarting moresuitable for starting the engine 10.

The above embodiments may be modified as follows.

The settings of the target working angle θt in the stop-time workingangle setting process at the time of both manual stop and automatic stopmay be changed as required according to the characteristics of the givenengine. If the target working angle θt of the intake valve 16 at thetime of a manual stop is set to such a value which allows forconceivable situations in which the engine will be restarted after bothautomatic stop and manual stop, it is possible to ensure proper enginestarting characteristics.

The working angle center φ may be varied between automatic stop andmanual stop. This permits the valve actuation of the intake valve 16 atrestart of the engine 10 to be finely adjusted. Consequently, thestarting characteristics of the engine 10 can be further improveddepending on the adjustment.

The target working angle θt at the stop-time working angle settingprocess of the above embodiments may be varied according to the enginestopping requirements in the automatic stop and manual stop. Forexample, if outside air temperature is very low when the engine stops,it is expected that the engine 10 is restarted at a very lowtemperature, and thus the target working angle θt may be set to asmaller value than when temperature is relatively high. In such a case,the present invention is also applicable to engines which do not performautomatic stop/restart control.

It may be after the engine 10 stops completely that the stop-timeworking angle setting process increases the working angle θ inpreparation for restarting. In this case, the cooperative control of thethrottle opening Ta performed along with increases in the working angleθ may be omitted. Also, the cooperative control of the throttle openingTa may also be omitted if variations in the rotational speed of theengine resulting from increases in the working angle θ are small.

The control for increasing the working angle θ when the engine stops canbe applied, in the same or similar manner as the above embodiments, toan engine which has only a variable working-angle control mechanism 19,but does not have a variable phase mechanism 18.

The present examples and embodiments are to be considered asillustrative and not restrictive and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

1. A valve actuation controlling apparatus applied to an engine equippedwith a variable working-angle control mechanism which varies workingangle of an intake valve, wherein, after commanding the engine to stop,the valve actuation controlling apparatus controls the variableworking-angle control mechanism to increase the working angle of theintake valve in preparation for restarting of the engine.
 2. The valveactuation controlling apparatus according to claim 1, wherein theapparatus adjusts a throttle opening of the engine in accordance withthe increase in the working angle of the intake valve after commandingthe engine to stop.
 3. A valve actuation controlling apparatus appliedto an engine equipped with a variable working-angle control mechanismwhich varies working angle of an intake valve, wherein, after commandingthe engine to stop, the valve actuation controlling apparatus controlsthe variable working-angle control mechanism to increase the workingangle of the intake valve in preparation for restarting of the engine,and varies the increased working angle according to whether a stoppingrequirement of the engine is satisfied.
 4. The valve actuationcontrolling apparatus according to claim 3, wherein the increasedworking angle is varied within a range where the valve closing time ofthe intake valve coincides with a middle period of a compression stroke.5. The valve actuation controlling apparatus according to claim 3,wherein the engine includes an ignition switch and performs automaticstop/restart control, wherein the engine stopping requirement comprises:an automatic stopping requirement that is satisfied when the engine isstopped by the automatic stop/restart control; and a manual stoppingrequirement that is satisfied when the ignition switch has been turnedoff, and the engine is stopped by the manual stopping requirement issatisfied, accordingly.
 6. The valve actuation controlling apparatusaccording to claim 5, wherein the increased working angle that has beenvaried in accordance with the automatic stopping requirement is largerthan the increased working angle that has been varied in accordance withthe manual stopping requirement.
 7. The valve actuation controllingapparatus according to claim 6, wherein the engine includes a cylinder,and wherein the increased working angle that has been varied inaccordance with the automatic stopping requirement is set to a maximumworking angle of the variable working-angle control mechanism, andwherein the increased working angle that has been varied in accordancewith the manual stopping requirement is equal to or lower than an upperlimit of a range in which a compression ratio of air in the cylinderdoes not cause knocking during a hot start of the engine, and is equalto or higher than a lower limit of a range in which a compression ratioof air in the cylinder permits a torque sufficient for a cold start ofthe engine to be generated.
 8. The valve actuation controlling apparatusaccording to claim 3, wherein the engine further includes a variablephase mechanism that varies a center of the working angle of the intakevalve, wherein, after commanding the engine to stop, the valve actuationcontrolling apparatus, in preparation for restarting of the engine, setsthe working angle center of the intake valve to a phase that is setaccording to the stopping requirement of the engine.
 9. The valveactuation controlling apparatus according to claim 3, wherein theapparatus adjusts a throttle opening of the engine in accordance withthe increase in the working angle of the intake valve after commandingthe engine to stop.
 10. An engine having a variable working-anglecontrol mechanism which varies working angle of an intake valve and avalve actuation controlling apparatus, wherein, after commanding theengine to stop, the valve actuation controlling apparatus controls thevariable working-angle control mechanism to increase the working angleof the intake valve in preparation for restarting of the engine.
 11. Theengine according to claim 10, wherein the valve actuation controllingapparatus adjusts a throttle opening of the engine in accordance withthe increase in the working angle of the intake valve after commandingthe engine to stop.
 12. An engine having a variable working-anglecontrol mechanism which varies working angle of an intake valve and avalve actuation controlling apparatus, wherein, after commanding theengine to stop, the valve actuation controlling apparatus controls thevariable working-angle control mechanism to increase the working angleof the intake valve in preparation for restarting of the engine, andvaries the increased working angle according to whether a stoppingrequirement of the engine is satisfied.
 13. The engine according toclaim 12, wherein the increased working angle is varied within a rangewhere the valve closing time of the intake valve coincides with a middleperiod of a compression stroke.
 14. The engine according to claim 12,further comprising an ignition switch, wherein the engine performsautomatic stop/restart control, wherein the engine stopping requirementcomprises: an automatic stopping requirement that is satisfied when theengine is stopped by the automatic stop/restart control; and a manualstopping requirement that is satisfied when the ignition switch has beenturned off, and the engine is stopped by the manual stopping requirementis satisfied, accordingly.
 15. The engine according to claim 14, whereinthe increased working angle that has been varied in accordance with theautomatic stopping requirement is larger than the increased workingangle that has been varied in accordance with the manual stoppingrequirement.
 16. The engine apparatus according to claim 15, furthercomprising a cylinder, wherein the increased working angle that has beenvaried in accordance with the automatic stopping requirement is set to amaximum working angle of the variable working-angle control mechanism,and wherein the increased working angle that has been varied inaccordance with the manual stopping requirement is equal to or lowerthan an upper limit of a range in which a compression ratio of air inthe cylinder does not cause knocking during a hot start of the engine,and is equal to or higher than a lower limit of a range in which acompression ratio of air in the cylinder permits a torque sufficient fora cold start of the engine to be generated.
 17. The engine according toclaim 12, further comprising a variable phase mechanism that varies acenter of the working angle of the intake valve, wherein, aftercommanding the engine to stop, the valve actuation controllingapparatus, in preparation for restarting of the engine, sets the workingangle center of the intake valve to a phase that is set according to thestopping requirement of the engine.
 18. The engine according to claim12, wherein the valve actuation controlling apparatus adjusts a throttleopening of the engine in accordance with the increase in the workingangle of the intake valve after commanding the engine to stop.
 19. Avalve actuation controlling method applied to an engine equipped with avariable working-angle control mechanism which varies working angle ofan intake valve, the method comprising: controlling the variableworking-angle control mechanism to increase the working angle of theintake valve in preparation for restarting of the engine, aftercommanding the engine to stop.
 20. The valve actuation controllingmethod according to claim 19, further comprising adjusting a throttleopening of the engine in accordance with the increase in the workingangle of the intake valve after commanding the engine to stop.
 21. Avalve actuation controlling method applied to an engine equipped with avariable working-angle control mechanism which varies working angle ofan intake valve, the method comprising: controlling the variableworking-angle control mechanism to increase the working angle of theintake valve in preparation for restarting of the engine, aftercommanding the engine to stop; and varying the increased working angleaccording to whether a stopping requirement of the engine is satisfied.22. The valve actuation controlling method according to claim 21,wherein said varying the increased working angle includes varying theincreased working angle within a range where the valve closing time ofthe intake valve coincides with a middle period of a compression stroke.23. The valve actuation controlling method according to claim 21,wherein the engine includes an ignition switch and performs automaticstop/restart control, wherein the engine stopping requirement comprises:an automatic stopping requirement that is satisfied when the engine isstopped by the automatic stop/restart control; and a manual stoppingrequirement that is satisfied when the ignition switch has been turnedoff, and the engine is stopped by the manual stopping requirement issatisfied, accordingly.
 24. The valve actuation controlling methodaccording to claim 23, wherein the increased working angle that has beenvaried in accordance with the automatic stopping requirement is largerthan the increased working angle that has been varied in accordance withthe manual stopping requirement.
 25. The valve actuation controllingmethod according to claim 24, wherein the engine includes a cylinder,and wherein the increased working angle that has been varied inaccordance with the automatic stopping requirement is set to a maximumworking angle of the variable working-angle control mechanism, andwherein the increased working angle that has been varied in accordancewith the manual stopping requirement is equal to or lower than an upperlimit of a range in which a compression ratio of air in the cylinderdoes not cause knocking during a hot start of the engine, and is equalto or higher than a lower limit of a range in which a compression ratioof air in the cylinder permits a torque sufficient for a cold start ofthe engine to be generated.
 26. The valve actuation controlling methodaccording to claim 21, wherein the engine further includes a variablephase mechanism that varies a center of the working angle of the intakevalve, the method comprising: setting, in preparation for restarting ofthe engine, the working angle center of the intake valve to a phase thatis set according to the stopping requirement of the engine aftercommanding the engine to stop.
 27. The valve actuation controllingmethod according to claim 21, further comprising adjusting a throttleopening of the engine in accordance with the increase in the workingangle of the intake valve after commanding the engine to stop.